Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus using the same.
Description of the Related Art
For a zoom lens to be used in an image pickup apparatus, it is expected that the zoom lens is small-sized, and that various aberrations are corrected favorably. On the other hand, for an image pickup element to be used in an image pickup apparatus, it is preferable that the image pickup element has a high sensitivity and that the number of pixels is large. For this, a size of the image pickup element (size of a light receiving surface) becomes large. For such reasons, a zoom lens, in addition to be small-sized and having various aberrations corrected favorably, is expected to be capable of coping with an image pickup element of a large size as well.
As the size of the image pickup element becomes large, a size of an image formed on the image pickup element also becomes large. To be capable of coping with an image pickup element of a large size means that, even in a case in which the size of the image has become large, various aberrations in a peripheral portion (a portion at a high image height) are corrected favorably.
Meanwhile, as a camera with a small size of image pickup element, small-sized cameras of a fixed-lens type (popularly known as compact cameras) have been used widely. As a zooming optical system appropriate for a fixed-lens camera, a zoom lens disclosed in Japanese Patent No. 3598971 is available. The zoom lens of Japanese Patent No. 3598971 includes four lens units. Concretely, the zoom lens includes in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a negative refractive power.
Incidentally, an arrangement in which, a lens unit having a positive refractive power is disposed nearest to an object is called as a positive-lead type arrangement. In the most basic positive-lead type arrangements, lens units are disposed from the object side in order of a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power.
The zoom lens of Japanese Patent No. 3598971 can be said to be a zoom lens in which, the positive refractive power of the fourth lens unit in the basic type is replaced by a negative refractive power. By doing so, in the zoom lens of Japanese Patent No. 3598971, at a telephoto end at which, the overall length tends to become long, an arrangement is made such that the desired zooming ratio is achieved while shortening the overall length of the zoom lens.
Moreover, in the past, as a camera with a large size of an image pickup area, silver-salt cameras were used widely. As a zoom lens to be used in a silver-salt camera, a zoom lens disclosed in Japanese Patent Application Laid-open Publication No. Hei 8-220438 is available. The zoom lens of Japanese Patent Application Laid-open Publication No. 220438 includes five lens units. Concretely, the zoom lens includes in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a negative refractive power.